1. Field of the Invention
The present invention generally relates to electrical circuitry and more particularly to improved thick film circuit composites such as microcircuit composites and methods of making the same.
2. Description of the Prior Art
Numerous techniques have been used to fabricate electrical circuitry and microcircuitry. One such technique is exemplified in U.S. Pat. No. 3,267,007 wherein a non-conductive substrate is coated with an adhesive resin. A film of metal is then deposited on the resin, as by vacuum deposition or electroless plating, whereupon the resin is cured from the B stage to the C stage, after which a plating resist is applied in a desired pattern over the metal film and plating on the desired metal is carried out. The procedure is lengthy and involved and still may result in poor adhesion to the substrate.
Another technique is disclosed in U.S. Pat. No. 3,653,946 wherein a gold film is formed and secured to a substrate by coating the substrate by a screen printing technique with a mixture of resinates, including gold resinate, and then heating the coated substrate at an elevated temperature to decompose the resinates. Such a technique is expensive and has limited applications.
A third technique is disclosed in U.S. Pat. No. 1,563,731 wherein a substrate of low melting point conductive material is covered with a thin meltable non-conductive film, after which a circuit pattern is cut through the film into the conductive material. Metal is then plated in the pattern, after which the non-conductive film and the substrate are melted away, leaving the desired circuit. This technique is not well adapted for fabrication of microcircuitry.
Still further techniques involve cutting or etching pattern in conductive materials, electroplating or electroless plating on conductive metal sheets, etc., depending on the particular characteristics and applications of the desired products.
One particularly useful technique involves screen printing a pattern of a thick paste of copper powder and a binder on a ceramic substrate and then firing the composite to form a desired thick film circuit pattern of the order of about 0.0005-0.001 inch thick. Unfortunately, when it is desired to weld, solder or otherwise high-temperature-bond wiring to the patterns, oxidation of the copper occurs, resulting in a bond which may have impaired electrical conductivity. It would be very desirable to overcome this drawback in a simple, inexpensive manner.